The proposed research is a molecular investigation of growth cone pathfinding mediated by the fasciclin 2 (Fas2) protein, with the long-term objective of understanding neural specificity by defining the biochemical mechanisms for cell-cell recognition in the developing central nervous system (CNS). The experimental approach is to study the expression and function of Fas2 by application of molecular and genetic methods primarily in the fruit fly Drosophila melanogaster, and cellular and anatomical techniques mainly in the grasshopper, Schistocerca americana. Fasciclin 2 is a cell surface glycoprotein isolated from grasshopper which is very similar in structure to vertebrate neural cell adhesion molecules (such as N-CAM, L1, contactin and myelin-associated glycoprotein), having 5 immunoglobulin-type domains and 2 fibronectin-like regions. It is expressed at first on a single longitudinal axon bundle in the CNS, and antibodies against it disrupt the formation of this axon bundle by retarding or blocking the initial fasciculation of its constituent axons. The specific goals of my proposal are these: (a) isolation and characterization of Fas2 cDNA and protein from Drosophila melanogaster; (b) isolation of the gene fo Fas2; and (c) isolation and characterization of Drosophila melanogaster which lack a functional Fas2 gene; and (d) determination of the biochemical mechanism of Fas2 action, including molecular structure-function studies on Fas2 in transfected cells and germ-line transformed Drosophila embryos. Al four specific aims will be approached initially by using the previously- characterized grasshopper Fas2 cDNA to isolate new Fas2 cDNA and genomic DN clones from Drosophila and grasshopper. Using standard techniques of molecular biology, these DNA fragments will be altered in specific ways and their function and expression tested after transfection into cell lines and into the Drosophila germ line. The discovery of Fas2 provides a unique opportunity to study a cell adhesion/recognition molecule using a potential ly powerful combination of molecular genetic, cell biological and anatomica methods in these model systems. The results from this project will help us understand how related molecules such as human N-CAM may function in brain development.